Per the request of area residents, beginning May 5th, 2015, TIRZ 17 opened a 30 day public comment period ending June 6, 2015, for the Memorial Drive Drainage and Mobility Improvements project. People can go to the home page of the TIRZ website and post their comments at www.houstontirz17.org. All questions and comments from the Town Hall Meeting and public comment period will be addressed and posted on their website within 60 days of closing date. This post presents some concepts that we would like to see incorporated in the Memorial Drive reconstruction project. Please feel free to borrow in whole or in part for your own comments.

For those that missed the TIRZ 17 Memorial Drive Town Hall Meeting April 14th, 2015, you can find the Power Point slide show here. The Memorial Drive reconstruction project will extend from Beltway 8 east almost to Tallowood and will add a sidewalk, a median, a 10-foot mixed-use shared hike and bike way, and over 10 acre-feet of underground detention. We applaud TIRZ 17 for designing a Complete Street, and for us a complete street includes improving the underground infrastructure when the less expensive opportunity presents itself, as during reconstruction. Below is a cross section of the planned roadway. Click on the drawing to open a clearer version.

Even though we consider this to be an improvement, we would like to offer some suggestions. First, it is important to consider what the priorities are for the roadway.

Our priorities are:

Safety – the road must be safe for motorists, bicyclists, and pedestrians;

Mobility – the road must convey through traffic smoothly while providing easy access to area homes and businesses, but it should not promote excessive speed;

Stormwater – this roadway must store excess stormwater runoff in an area known to have serious flooding problems;

Quality of Life – the roadway should mirror the lush landscape and amenities for which the Memorial area is known.

From a safety standpoint, it’s best to separate pedestrians and bicyclists from the roadway by trees – better to hit a tree than a person. As the trees grow, their canopy not only provides shade, air filtration, and noise reduction, but the presence of a canopy also encourages drivers to slow down and psychologically conveys the impression of a higher quality of life to an area. Perhaps equally important, as trees grow it becomes increasingly more difficult and expensive to widen the road because the trees must be replaced by trees with girth equivalence.

Traffic studies of Memorial Drive do not justify widening the roadway to more than four lanes, however, inserting a 24 foot median easily allows the roadway to be widened at a later date. When the TIRZ raised the possibility of taking the Gessner esplanade for underground detention, even if it was to be replaced and replanted, neighbors vociferously objected – and rightfully so. The esplanades along Gessner and other Memorial roadways are one of the reasons the area is such a desirable place to live, but they are always vulnerable to road widening (see Project ID 12282).

If that is so, then why create an esplanade as a placeholder for a future road widening? Lane widths for a major Houston thoroughfare are generally defined as 11 feet wide. A 24-foot esplanade therefore allows two lanes of 12 feet each with only stripe separation or two 11-foot lanes with a 2-foot raised separator. If it is desired that the esplanade never be removed, then it needs to be too narrow to create two lanes; that is, it needs to be 20 feet or less. Combined with trees between the street and sidewalks, a 20-foot esplanade would make it difficult to remove the median or widen the roadway. Ostensibly, a two way left turn lane (affectionately called suicide lanes) could be added, but it seems unlikely. Suicide lanes are a serious source of accident fatalities, so should be avoided whenever possible.

A 20 foot esplanade also frees 4 feet of the 100-foot Right of Way (ROW) that can be used elsewhere. We have elected to use the 4 feet to expand the 6-foot sidewalk into another 10-foot mixed-use shared hike and bike way on the north side. The graphic shows the widened sidewalks, a 20-foot median, and trees placed between the street and sidewalks. Hopefully, our reasons for these changes will become more obvious. Again, clicking on the graphic opens a larger version.

Porous concrete has begun to make inroads into some areas of building. Rice University has paved many of their sidewalks with porous concrete and it is used in the parking lot at Frostwood Elementary. So we asked ourselves, why not make the 10-foot sidewalks of porous material and install underground retention? If the soil quality was sufficient at Frostwood to support a similar underground system, certainly it would also be expected to work less than a mile away. The graphic to the right indicates how this would work. These systems are finding their way into design manuals in many communities, including Houston, where they are being used in lieu of surface detention systems.

Below is a quote that we presented to the Houston City Council’s Transportation, Technology, and Infrastructure (TTI) Committee when the City proposed replacing sidewalks for homeowners. This system costs approximately the same that then Public Works and Engineering (PW&E) Director, Dan Kruger, testified before the Committee that the City would charge to install a sidewalk. A permeable sidewalk is not a detention system and does not need continuous connections so pipes and communication lines don’t interfere. Because it is an open bottomed pipe, it also recharges the aquifer and water eventually percolates into the soil, reducing the possibility for mosquito breeding. Concrete pipes are notorious breeding grounds for mosquitoes. Puddling is eliminated with porous sidewalks, so bicyclists can use the sidewalk just after the rain without spraying “rooster-tails” over themselves and everyone else.

We got a quote from Triton because they happened to answer the phone when we called and were willing to provide this information. Residents Against Flooding has no affiliation whatsoever with Triton. Moreover, there are numerous other companies producing similar systems [1], [2],[3] so this technology clearly works and is readily available. It’s useful to note that if the ground is deemed to have a poor water infiltration rate, then this system can serve as more flexible normal detention, although the chambers would then need to be interconnected.

In the PowerPoint presentation, LAN states that over 10 acre-feet of detention can be achieved using dual underground 10-foot by 10-foot rectangular culverts. In a 100-foot ROW, more than two rows of culverts can be installed. Can we add more? Is it a matter of construction difficulty or the cost of the culverts?

Suppose that additional 10-foot by 10-foot pipes extending from W153 were placed under the permeable sidewalk drainage system. These would not be used to convey water, but would be used to add capacity to W153. Therefore, they would be closed at one end and fully open to W153 at four places where it crosses under Memorial Drive underneath the north and south sidewalks: two would connect under the bridge underneath the southern 10-foot sidewalk with one extending east and the other extending west; and two more underneath the northern sidewalk – again, one east and one west. The graphic to the right shows the concept. Since they add capacity, they would dead-ended some practical distance east or west of the W153 bridge and need to be sloped so that water would drain back into the channel after a rain event. A 1% slope is probably sufficient, meaning that the elevation of top of the pipe rises 1 foot for every 100 feet of pipe.

To the right is a picture of W153 at Memorial Drive. There is a 9-foot by 9-foot channel under the roadway; the smaller pipe was added to compensate for lost capacity due to bisection of the main channel by a large water line and reconnects into the main pipe under the roadway. Hopefully, much of this will be corrected in the Memorial Drive redesign. For reference, nearby residents measured the distance from the bridge surface to the channel bottom at 23 feet, so there should be sufficient space under the sidewalk drainage system, which takes about 5 feet, even if the roadway is lowered. For every 217 feet that a pair of these pipes extend, one acre-feet of detention is added. Since elevations rise more to the west, it’s expected that more capacity can be added in that direction. During construction, fill dirt around the pipes can be selected to complement operation of the sidewalk drainage system. Again, these pipes are in addition to the drainage systems currently planned by the TIRZ.